Infertility is a common health problem that affects 10-15% of couples of reproductive-age. In the United States alone in the year 2006, approximately 140,000 cycles of in vitro fertilization (IVF) were performed (cdc.gov/art). This resulted in the culture of more than a million embryos annually with variable, and often ill-defined, potential for implantation and development to term. The live birth rate, per cycle, following IVF was just 29%, while on average 30% of live births resulted in multiple gestations (cdc.gov/art). Multiple gestations have well-documented adverse outcomes for both the mother and fetuses, such as miscarriage, pre-term birth, and low birth rate. Potential causes for failure of IVF are diverse; however, since the introduction of IVF in 1978, one of the major challenges has been to identify the embryos that are most suitable for transfer and most likely to result in term pregnancy.
The understanding in the art of basic embryo development is limited as studies on human embryo biology remain challenging and often exempt from research funding. Consequently, most of the current knowledge of embryo development derives from studies of model organisms. Embryos from different species go through similar developmental stages, however, the timing varies by species. These differences and many others make it inappropriate to directly extrapolate from one species to another. (Taft, R. E. (2008) Theriogenology 69(1):10-16). The general pathways of human development, as well as the fundamental underlying molecular determinants, are unique to human embryo development. For example, in mice, embryonic transcription is activated approximately 12 hours post-fertilization, concurrent with the first cleavage division, whereas in humans embryonic gene activation (EGA) occurs on day 3, around the 8-cell stage (Bell, C. E., et al. (2008) Mol. Hum. Reprod. 14:691-701; Braude, P., et al. (1988) Nature 332:459-461; Hamatani, T. et al. (2004) Proc. Natl. Acad. Sci. 101:10326-10331; Dobson, T. et al. (2004) Human Molecular Genetics 13(14):1461-1470). In addition, the genes that are modulated in early human development are unique (Dobson, T. et al. (2004) Human Molecular Genetics 13(14):1461-1470). Moreover, in other species such as the mouse, more than 85% of embryos cultured in vitro reach the blastocyst stage, one of the first major landmarks in mammalian development, whereas cultured human embryos have an average blastocyst formation rate of approximately 30-50%, with a high incidence of mosaicism and aberrant phenotypes, such as fragmentation and developmental arrest (Rienzi, L. et al. (2005) Reprod. Biomed. Online 10:669-681; Alikani, M., et al. (2005) Mol. Hum. Reprod. 11:335-344; Keltz, M. D., et al. (2006) Fertil. Steril. 86:321-324; French, D. B., et al. (2009) Fertil. Steril.). In spite of such differences, the majority of studies of preimplantation embryo development derive from model organisms and are difficult to relate to human embryo development (Zernicka-Goetz, M. (2002) Development 129:815-829; Wang, Q., et al. (2004) Dev Cell. 6:133-144; Bell, C. E., et al. (2008) Mol. Hum. Reprod. 14:691-701; Zernicka-Goetz, M. (2006) Curr. Opin. Genet. Dev. 16:406-412; Mtango, N. R., et al. (2008) Int. Rev. Cell. Mol. Biol. 268:223-290).
Traditionally in IVF clinics, human embryo viability has been assessed by simple morphologic observations such as the presence of uniformly-sized, mononucleate blastomeres and the degree of cellular fragmentation (Rijinders P M, Jansen C A M. (1998) Hum Reprod 13:2869-73; Milki A A, et al. (2002) Fertil Steril 77:1191-5). More recently, additional methods such as extended culture of embryos (to the blastocyst stage at day 5) and analysis of chromosomal status via preimplantation genetic diagnosis (PGD) have also been used to assess embryo quality (Milki A, et al. (2000) Fertil Steril 73:126-9; Fragouli E, (2009) Fertil Steril June 21 [EPub ahead of print]; El-Toukhy T, et al. (2009) Hum Reprod 6:20; Vanneste E, et al. (2009) Nat Med 15:577-83). However, potential risks of these methods also exist in that they prolong the culture period and disrupt embryo integrity (Manipalviratn S, et al. (2009) Fertil Steril 91:305-15; Mastenbroek S, et al. (2007) N Engl J Med. 357:9-17).
U.S. Pat. Nos. 7,963,906; 8,323,177 and 8,337,387 describe novel timing parameters including the duration of the first cytokinesis, the interval between cytokinesis 1 and cytokinesis 2, the interval between mitosis 1 and mitosis 2, the interval between cytokinesis 2 and cytokinesis 3 and the interval between mitosis 2 and mitosis 3 that are useful in selecting embryos with good developmental potential that are likely to reach the blastocyst stage, implant into the uterus and/or be born live.
Not withstanding the recent developments in time lapse imaging that allow clinicians to select embryos with greater developmental potential based on timing parameters of the first few cell cycles, current embryo selection relies primarily on morphological evaluations which are very subjective and offer limited predictive value of embryo viability. Failure to correctly identify the most viable embryos can lead to unsuccessful IVF treatment or multiple gestation pregnancy. Time-lapse imaging technology allows real time embryo monitoring and provides additional insight into human embryo developmental biology. This technology has allowed for the identification of new atypical embryo phenotypes and new timing parameters that may impact embryo development including the novel syngamy parameters described herein.